Available online at www.sciencedirect.com Communications in Nonlinear Science and Numerical Simulation 14 (2009) 2469–2481 www.elsevier.com/locate/cnsns Environmental flow requirements for integrated water resources allocation in the Yellow River Basin, China Z.F. Yang a,*, T. Sun a, B.S. Cui a, B. Chen a, G.Q. Chen b a State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China b National Laboratory for Complex Systems and Turbulence, Department of Mechanics, Peking University, Beijing 100871, China Received 9 May 2007; received in revised form 16 October 2007; accepted 12 December 2007 Available online 29 February 2008 Abstract Based on the classification and regionalization of the ecosystem, multiple ecological management objectives and the spatial variability of the environmental flow requirements of the Yellow River Basin were analyzed in this study. The sum- mation rule was used to calculate water consumption requirements and the compatibility rule, i.e., ‘‘maximum” principle, was also adopted to estimate the non-consumptive use of water in the river basin. The environmental flow requirements for integrated water resources allocation were determined by identifying the natural and artificial water consumption in the Yellow River Basin. The results indicated that the annual minimum environmental flow requirements amounted to 317.62 Â 108 m3, which represented 54.76% of the natural river flows, while for the environmental flow requirements for the integrated water resources allocation were 262.47 Â 108 m3, which represented 45.25% of the natural river flows. The highest percentage of environmental flow requirements was 93.64% for the river ecosystem. It can be concluded that the primary concerns should be put on the downstream river water requirements to determine the environmental flows for integrated water resources allocation in a river basin. Ó 2008 Elsevier B.V. All rights reserved. PACS: 92.40.Qk; 92.10.Sx Keywords: Environmental flow requirements; Water resources allocation; Consumptive water use; Yellow River Basin 1. Introduction To maintain the healthy and sustainable development of a river basin, the focus of water resources alloca- tion has been put on the water supply for human needs, with little attention to the environment [1]. Mean- while, large amount of water should be left in or released into an aquatic ecosystem for environmental protection has been occupied for human needs in recent years. For example, up to 50% of the flow from the Sacramento–San Joaquin River system that empties into the San Francisco Bay is diverted out of the * Corresponding author. Tel.: +86 10 58807951; fax: +86 10 58800397. E-mail address: [email protected] (Z.F. Yang). 1007-5704/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cnsns.2007.12.015 2470 Z.F. Yang et al. / Communications in Nonlinear Science and Numerical Simulation 14 (2009) 2469–2481 channel before it reaches the bay [2]. The over-demand of freshwater is often more urgent in developing coun- tries, such as China. Freshwater discharge into the Yellow River, which is the second largest river in China, has decreased 72% between the 1960s and 1990s [3]. Therefore, environmental flows have been increasingly recognized as a central issue in sustainable water resources management [4]. Environmental flow requirement (EFR) for water resources allocation requires that a certain amount of water be purposefully left in or released into an aquatic ecosystem to maintain it in a con- dition that will support its direct and indirect use values [5]. Maintenance of EFR has also become one of the highest priorities of the management of the Yellow River Basin [6]. To assess how much of the original flow regime of a river should continue to flow down it to maintain the riverine ecosystem health, a growing number of countries now recognize the need for studying EFR and incorporating EFR into water resources manage- ment [7]. Considering the differences among ecosystem structures, EFR studies have been conducted for rivers, wet- lands, forest and grassland ecosystem, as well as in cities and estuaries [8–11]. Since the 1970s, there has been a progressive evolution of methodologies for assessing the EFR of riverine, wetlands and estuarine ecosystems. Different kinds of methodologies, including hydrological index, hydraulic rating, habitat simulation and holis- tic ones, have been widely used [12]. Hydrological methods use flow data to estimate the EFR, which are regarded as providing low confidence EFR estimates, when there is insufficient quantitative information about how different aquatic species respond to variations of hydrological indices. Instream habitat modelling meth- ods, such as Instream Flow Incremental Methodology (IFIM), are based on the determination of habitat pref- erence curves for species [13]. Also, habitat availability is modelled for change in discharge [14]. Considering the differences in ecosystem functions, methodology for determining the EFRs will also vary for ecosystems with different objectives on environmental production [15]. Richter et al. [16] proposed an approach for setting streamflow-based river ecosystem management targets and RVA methods concerning the spatial variation of hydrological parameters and associated characteristics of timing, frequency, duration and rates of change, in sustaining aquatic ecosystems. Parameters of geomorphology, land use, soils, climate and vegetation were considered in the study of the eco-region for describing water quality patterns in a basin [17]. River zones (confined zone, armour zone, mobile zone, meander zone and anastomosing zone) and eco- logically important flows levels were identified for determining environmental water allocations in the Cond- amine–Balonne River in Australia [18]. Considering multiple ecological management objectives, spatial variability among ecosystems and influ- ences of hydraulic works, classification and regionalization of the aquatic ecosystem are analyzed in this paper. Then, the environmental flows are determined for integrated water resources allocation in the Yellow River Basin. Finally, based on the comparison between the EFR with the water utilization in water resources allocation, suggestions for water resource management of the Yellow River Basin are presented. 2. Integrated EFRs for basin 2.1. Classification of EFRs for basin EFR can be divided into a range of different categories in order to maintain the health of ecosystem with different structures. Terrestrial ecosystems (e.g., forest and grassland) and wetland ecosystems (e.g., riverine habitats) have different EFRs. Considering the different functions of river flow, in terms of both quantity and quality, as well as their temporal variability, the EFRs can be classified into several main components in a river basin as shown in Table 1. The EFR for a basin can be divided into consumptive and non-consumptive water volumes, which can be allocated as needed by managers to meet diverse ecological objectives. The quantities of water needed to ensure the replacement of evapotranspiration by vegetation, soil moisture, and evaporative losses, and to ensure the maintenance of appropriate surface areas and water depths for stability of wetland habitats, are considered consumptive uses and are mainly fulfilled by the natural precipitation. Water needed to maintain the requirements of riverine habitat and to provide adequate transport of sediments and nutrients is consid- ered as non-consumptive use, and represents the river’s flow, which are mainly influenced by the water utilization. Z.F. Yang et al. / Communications in Nonlinear Science and Numerical Simulation 14 (2009) 2469–2481 2471 Table 1 Classification system of EFRs for basin First grade Second grade Functions Terrestrial EFRs for forest and Water requirements for evapotranspiration of vegetation, soil moisture, etc. ecosystems grass lands EFRs for Urban Greenbelt Wetland EFRs for rivers Water requirements for base flow,evaporation from water surfaces, infiltration, dilution, ecosystems EFRs for lakes sediment transport, the maintenance of riverine habitat, etc. EFRs for urban wetlands EFRs for estuaries Water requirements for freshwater wetlands, balance of salinity, sediment and nutrients, etc. 2.2. Regionalization of EFRs for basin Besides the variability of the structures, there is also spatial variability of the ecological functions among ecosystems with different ecological objectives. To identify the ecological objectives for different ecosystems in a river basin, regionalization of the river system is necessary for determining the EFRs concerning different natural factors (e.g., hydrology and climate) and anthropocentric factors (e.g., hydraulic works). There is com- patibility between the non-consumptive water requirements for different regions connected by the hydrological process in basin. The index system of regionalization of river system for determining the EFRs in the river basin is shown in Table 2. 2.3. EFRs for integrated water resources allocation Due to the different ecosystems with various structures and functions, the EFRs should be allocated as needed by managers to meet diverse ecological objectives. However, the total environmental flows are not just the sum of the EFRs with different objectives. In this paper, the summation rule is used for calculating con- sumptive water requirements, i.e., the requirements for each category of water use. In contrast, the compat- ibility rule (or termed the ‘‘maximum”